Unzip the libpng for Android downloaded file. Go to [LIBPNG_FOR_ANDROID_FOLDER]/jni/ and using a text editor open file config.h. Find the values for the following 3 variables PACKAGE_STRINGPACKAGE_VERSIONVERSION and make sure that they have the correct version number. At the time this post was written, the author of the repository omitted to update those values from 1.4.1 to 1.6.23. (
config.h (compressed) (198 downloads)
)

Using a terminal go into the folder that was created and execute: ./build.sh

In case you get the error ./build.sh: line 2: ndk-build: command not found then edit build.sh using a text editor and on line 2 add the full path to the file ndk-build that is in the folder of the Android NDK you unzipped before. After you do this change execute ./build.sh again.

Inside each of the folders in [LIBPNG_FOR_ANDROID_FOLDER]/obj/local/ you will find a file called libpng.a.
Copy those files while renaming them to liblibpng.a into the respective folders of the OpenCV library you are using in you project that are found here [OPENCV_FOLDER]/sdk/native/3rdparty/libs/.
Inside [LIBPNG_FOR_ANDROID_FOLDER]/obj/local/ we found the following folders: arm64-v8a, armeabi, armeabi-v7a, mips, mips64, x86, x86_64.
We did not use all of them as in [OPENCV_FOLDER]/sdk/native/3rdparty/libs/ we only had armeabi, armeabi-v7a, mips, x86.

Rebuild your applications, test them and if they are OK upload the new versions online.

Hello Google Play Developer,

We detected that your app(s) listed at the end of this email are using an unsafe version of the libpng library. Apps with vulnerabilities like this can expose users to risk of compromise and may be considered in violation of our Malicious Behavior policy.

What’s happening

Beginning September 17, 2016, Google Play will block publishing of any new apps or updates that use vulnerable versions of libpng. Your published APK version will not be affected, however any updates to the app will be blocked unless you address this vulnerability.

Action required: Migrate your app(s) to use libpng v1.0.66, v.1.2.56, v.1.4.19, v1.5.26 or higher as soon as possible and increment the version number of the upgraded APK.

Check back after five hours – we’ll show a warning message if the app hasn’t been updated correctly.

The vulnerability stems from an out of bounds memory access that could potentially lead to code execution. Versions 1.0.x before 1.0.66, 1.1.x and 1.2.x before 1.2.56, 1.3.x and 1.4.x before 1.4.19, and 1.5.x before 1.5.26 are affected.

You can read more about the vulnerability in CVE-2015-8540. For other technical questions about the vulnerability, you can post to Stack Overflow and use the tag “android-security.”

While these specific issues may not affect every app that uses libpng, it’s best to stay up to date on all security patches.https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2015-8540

Affected app(s) and version(s) are listed below. If you have more than 20 affected apps in your account, please check the Developer Console for a full list.

net.bytefreaks.opencvfacerecognition 1

Related post by Google Play Team:

How to fix apps containing Libpng Vulnerability

This information is intended for developers of apps that utilize any version of libpng library, that contains a security vulnerability disclosed in CVE-2015-8540. Apps with vulnerabilities like this can expose users to risk of compromise and may be considered in violation of our Malicious Behavior policy.

Please migrate your app(s) to libpng v1.0.66, v.1.2.56, v.1.4.19, v1.5.26 or higher as soon as possible and increment the version number of the upgraded APK. Beginning Sep 17, 2016, Google Play will block publishing of any new apps or updates that use vulnerable versions of libpng. Your published app version will remain unaffected, however any updates to the app will be blocked unless they address this vulnerability.

Check back after five hours – we’ll show a warning message if the app hasn’t been updated correctly. Note that some processing delays are common even if your app has fixed the vulnerability.

The vulnerability stems from an out of bounds memory access that could potentially lead to code execution. Versions 1.0.x before 1.0.66, 1.1.x and 1.2.x before 1.2.56, 1.3.x and 1.4.x before 1.4.19, and 1.5.x before 1.5.26 are affected.
You can read more about the vulnerability in CVE-2015-8540.

For other technical questions, you can post to Stack Overflow and use the tags “android-security”. Note that questions about Play policy should not be posted to Stack Overflow.

#!/bin/bash
#This script will merge two jpg images into one using imageMagick.
#The final result will be a picture that is split diagonally.
#The diagonal line will start from the top left of the image.
#Both pictures must be of the same size.
#If you do not give the filenames as part of the command line, the default names will be used (Left.jpg and Right.jpg).
#If command line argument 1 is not provided, the value will default to the variable $LEFT_DEFAULT
LEFT_DEFAULT="Left.jpg";
LEFT=${1:-$LEFT_DEFAULT};
#If command line argument 2 is not provided, the value will default to the variable $Right_DEFAULT
RIGHT_DEFAULT="Right.jpg";
RIGHT=${2:-$RIGHT_DEFAULT};
#The intermediate images we will use must be png to support transparency.
#We remove the extension '.jpg' from the filenames and add the extension '.png'.
LEFT_OUT="${LEFT%.jpg}.Diagonal Down - Mask.png";
RIGHT_OUT="${RIGHT%.jpg}.Diagonal Down - Mask.png";
OUT="Diagonal Down - Mask.jpg";
#Read the width of one of the images;
WIDTH=`identify -format %w "$LEFT"`;
#Read the height of one of the images;
HEIGHT=`identify -format %h "$LEFT"`;
convert -respect-parenthesis \
\( "$LEFT" -gravity north -crop "$WIDTH"x"$HEIGHT"+0+0 +repage -write "$LEFT_OUT" \) `#Load first image to a new png` \
\( "$RIGHT" -gravity east -crop "$WIDTH"x"$HEIGHT"+0+0 +repage -write "$RIGHT_OUT" \) `#Load second image to a new png` \
\( -size "$WIDTH"x"$HEIGHT" xc:black -fill white -draw "polygon 0,0 "$WIDTH","$HEIGHT" 0,"$HEIGHT"" -write "MASK_$LEFT_OUT" \) `#Create the mask of the lower triangle` \
\( -clone 2 -negate -write "MASK_$RIGHT_OUT" \) `#Create the mask of the upper triangle` \
\( -clone 0 -clone 2 -alpha off -compose copy_opacity -composite -write "$LEFT_OUT" \) `#Apply the upper triangle mask to the left image` \
\( -clone 1 -clone 3 -alpha off -compose copy_opacity -composite -write "$RIGHT_OUT" \) `#Apply the lower triangle mask to the right image` \
-delete 0-3 -compose over -composite "$OUT" `#Merge the two images together`;
#Cleaning up
rm "MASK_$RIGHT_OUT" "MASK_$LEFT_OUT" "$LEFT_OUT" "$RIGHT_OUT";

#!/bin/bash
#This script will merge two jpg images into one using imageMagick.
#The final result will be a picture that is split diagonally.
#The diagonal line will start from the bottom left of the image.
#Both pictures must be of the same size.
#If you do not give the filenames as part of the command line, the default names will be used (Left.jpg and Right.jpg).
#If command line argument 1 is not provided, the value will default to the variable $LEFT_DEFAULT
LEFT_DEFAULT="Left.jpg";
LEFT=${1:-$LEFT_DEFAULT};
#If command line argument 2 is not provided, the value will default to the variable $Right_DEFAULT
RIGHT_DEFAULT="Right.jpg";
RIGHT=${2:-$RIGHT_DEFAULT};
#The intermediate images we will use must be png to support transparency.
#We remove the extension '.jpg' from the filenames and add the extension '.png'.
LEFT_OUT="${LEFT%.jpg}.Diagonal Up - Mask.png";
RIGHT_OUT="${RIGHT%.jpg}.Diagonal Up - Mask.png";
OUT="Diagonal Up - Mask.jpg";
#Read the width of one of the images;
WIDTH=`identify -format %w "$LEFT"`;
#Read the height of one of the images;
HEIGHT=`identify -format %h "$LEFT"`;
convert -respect-parenthesis \
\( "$LEFT" -gravity north -crop "$WIDTH"x"$HEIGHT"+0+0 +repage -write "$LEFT_OUT" \) `#Load first image to a new png` \
\( "$RIGHT" -gravity east -crop "$WIDTH"x"$HEIGHT"+0+0 +repage -write "$RIGHT_OUT" \) `#Load second image to a new png` \
\( -size "$WIDTH"x"$HEIGHT" xc:black -fill white -draw "polygon 0,0 0,"$HEIGHT" "$WIDTH",0" -write "MASK_$LEFT_OUT" \) `#Create the mask of the upper triangle` \
\( -clone 2 -negate -write "MASK_$RIGHT_OUT" \) `#Create the mask of the lower triangle` \
\( -clone 0 -clone 2 -alpha off -compose copy_opacity -composite -write "$LEFT_OUT" \) `#Apply the upper triangle mask to the left image` \
\( -clone 1 -clone 3 -alpha off -compose copy_opacity -composite -write "$RIGHT_OUT" \) `#Apply the lower triangle mask to the right image` \
-delete 0-3 -compose over -composite "$OUT" `#Merge the two images together`;
#Cleaning up
rm "MASK_$RIGHT_OUT" "MASK_$LEFT_OUT" "$LEFT_OUT" "$RIGHT_OUT";

Older Attempts with Black Line in the Middle

#!/bin/bash
#This script will merge two jpg images into one using imageMagick.
#The final result will be a picture that is split diagonally.
#The diagonal line will start from the top left of the image.
#Both pictures must be of the same size.
#If you do not give the filenames as part of the command line, the default names will be used (Left.jpg and Right.jpg).
#If command line argument 1 is not provided, the value will default to the variable $LEFT_DEFAULT
LEFT_DEFAULT="Left.jpg";
LEFT=${1:-$LEFT_DEFAULT};
#If command line argument 2 is not provided, the value will default to the variable $Right_DEFAULT
RIGHT_DEFAULT="Right.jpg";
RIGHT=${2:-$RIGHT_DEFAULT};
#The intermediate images we will use must be png to support transparency.
#We remove the extension '.jpg' from the filenames and add the extension '.png'.
LEFT_OUT="${LEFT%.jpg}.Diagonal Down.png";
RIGHT_OUT="${RIGHT%.jpg}.Diagonal Down.png";
OUT="Diagonal Down.jpg";
#Read the width of one of the images;
WIDTH=`identify -format %w "$LEFT"`;
#Read the height of one of the images;
HEIGHT=`identify -format %h "$LEFT"`;
OFFSET=1;
WIDTH_M=$((WIDTH-OFFSET));
HEIGHT_M=$((HEIGHT-OFFSET));
#We create a transparent triangle on the side of the image we do not want visible.
#A problem that arises here: we create a triangle with no fill, which turns black. Then we fill that area to make it transparent, since the image is a jpg some of the newly created black pixels do not get removed. When merging the two images, this creates a black diagonal line in the middle.
convert "$LEFT" -gravity north -crop "$WIDTH"x"$HEIGHT"+0+0 +repage \
-draw "polygon 0,0 "$WIDTH","$HEIGHT" "$WIDTH",0 fill none matte "$WIDTH_M","$OFFSET" floodfill" \
\( +clone -channel RGBA \) \
-compose DstOver -composite "$LEFT_OUT";
#We create a transparent triangle on the side of the image we do not want visible.
convert "$RIGHT" -gravity north -crop "$WIDTH"x"$HEIGHT"+0+0 +repage \
-draw "polygon "$WIDTH","$HEIGHT" 0,0 0,"$HEIGHT" fill none matte "$OFFSET","$HEIGHT_M" floodfill" \
\( +clone -channel RGBA \) \
-compose DstOver -composite "$RIGHT_OUT";
#We merge the two images together.
composite -blend 50% "$LEFT_OUT" "$RIGHT_OUT" "$OUT";
#Cleaning up
rm "$LEFT_OUT" "$RIGHT_OUT";

#!/bin/bash
#This script will merge two jpg images into one using imageMagick.
#The final result will be a picture that is split diagonally.
#The diagonal line will start from the bottom left of the image.
#Both pictures must be of the same size.
#If you do not give the filenames as part of the command line, the default names will be used (Left.jpg and Right.jpg).
#If command line argument 1 is not provided, the value will default to the variable $LEFT_DEFAULT
LEFT_DEFAULT="Left.jpg";
LEFT=${1:-$LEFT_DEFAULT};
#If command line argument 2 is not provided, the value will default to the variable $Right_DEFAULT
RIGHT_DEFAULT="Right.jpg";
RIGHT=${2:-$RIGHT_DEFAULT};
#The intermediate images we will use must be png to support transparency.
#We remove the extension '.jpg' from the filenames and add the extension '.png'.
LEFT_OUT="${LEFT%.jpg}.Diagonal Up.png";
RIGHT_OUT="${RIGHT%.jpg}.Diagonal Up.png";
OUT="Diagonal Up.jpg";
#Read the width of one of the images;
WIDTH=`identify -format %w "$LEFT"`;
#Read the height of one of the images;
HEIGHT=`identify -format %h "$LEFT"`;
OFFSET=1;
WIDTH_M=$((WIDTH-OFFSET));
HEIGHT_M=$((HEIGHT-OFFSET));
#We create a transparent triangle on the side of the image we do not want visible.
#A problem that arises here: we create a triangle with no fill, which turns black. Then we fill that area to make it transparent, since the image is a jpg some of the newly created black pixels do not get removed. When merging the two images, this creates a black diagonal line in the middle.
convert "$LEFT" -gravity north -crop "$WIDTH"x"$HEIGHT"+0+0 +repage \
-draw "polygon "$WIDTH","$HEIGHT" 0,"$HEIGHT" "$WIDTH",0 fill none matte "$WIDTH_M","$HEIGHT_M" floodfill" \
\( +clone -channel RGBA -blur 1x65000 \) \
-compose DstOver -composite "$LEFT_OUT";
#We create a transparent triangle on the side of the image we do not want visible.
convert "$RIGHT" -gravity north -crop "$WIDTH"x"$HEIGHT"+0+0 +repage \
-draw "polygon 0,0 0,"$HEIGHT" "$WIDTH",0 fill none matte "$OFFSET","$OFFSET" floodfill" \
\( +clone -channel RGBA -blur 1x65000 \) \
-compose DstOver -composite "$RIGHT_OUT";
#We merge the two images together.
composite -blend 50% "$LEFT_OUT" "$RIGHT_OUT" "$OUT";
#Cleaning up
rm "$LEFT_OUT" "$RIGHT_OUT";

The scary looking creature photographed is a fictional character from the Warcraft franchise and it is called a Murloc:

The murlocs are amphibious bipedal fish-like creatures, which dwell along the coastlines of the Eastern Kingdoms, and few other locations. Little is known about this species, although they seemingly have enough intellect to form societies and tribes, even having their own faith system. They have their own spoken language, although it is unpronounceable in the common tongue.
— From Wikipedia: https://en.wikipedia.org/wiki/Races_and_factions_of_Warcraft#Murlocs

In this gallery we added along with the original and the filtered pictures some more that use half of the original picture and half of the filtered picture to better show how the effect altered the original picture.

Notes:

Prisma only accepts square images and it will resize the produced result to 1080px if the input image is larger than that.